REQUIREMENT of Air Preheater REQUIREMENT of Air Preheater

REQUIREMENT of Air Preheater
Air preheater is an important boiler auxiliary, the placeholder in the first line of the
combustion air for rapid and efficient combustion in the furnace. The air heater recovers
heat from the outgoing flue gas of a boiler and transmits them to the combustion air
In a useful boiler, the flue gas leaves the economizer at a temperature of about
3800 C. Since every 550C drop in the flue gas temperature increases the boiler efficiency by
about 2.5%, the boiler efficiency is significantly improved with an air heater downstream of
economizer. Furthermore, the air heater can also be used for heating the air to dry the coal
in the pulverization plant.
Advantages of using air heaters
The recovery of waste heat from the flue gas and the heating of the boiler air in an
air heater offers the following advantages.
a) the boiler efficiency is increased.
b) more stable combustion in the furnace.
c) the combustion is reinforced using hot air.
d) lower coal grades can be burned efficiently with hot air.
e) the use of hot air improves the heat transfer rate and thus less heat transfer area
required.
f) the combustion is complete with negligible amount of carbon in ash.
g) Faster load fluctuations are possible.
h) the coal can be effectively dried for easy pulverization and combustion.